Bad NCE Power Cab.

[dasatcopthorne]

Guys.

 

Check out this behaviour when plugging in.

It works perfectly as a slave to another Cab.

 

All wiring checked as OK.

 

Also, is there a component missing in the centre of the still pic above the word 'GND'. Should it we a line of four?

Voltage regulator has been replaced just in case.

Is there a known mod for the Power Cab.

 

Lastly, I backdated it to an old V1.23 chip. Makes no difference.

 

Dave.

 

 

Edited May 21, 2023 by dasatcopthorne

[woodenhead]

Has it been altered to be a Pro Cab which will only work with a command station?

 

There appears to be a lot of third party solder on there, is that by you or was it like that when you purchased it, who did you purchase it from?

[melmerby]

Looks a bit of a mess. Have some of the power devices been replaced - not the 5v regulator

Those 4-in-a row, look like they should be four resistors in parallel, most likely all four the same value but they look like they've been overloaded and there is just the remains of one of them.

 

 

 

Edited May 21, 2023 by melmerby

[woodenhead]

This is what they look like normally,  a lot neater.

 

Image from http://www.hall-royd-junction.co.uk/Hall_Royd_Model/layout_28.html

Edited May 21, 2023 by woodenhead
Added source for image.

[jpendle]

It looks like all 4 of those resistors have been subject to mechanical damage. They should all be replaced but I don’t know what with.

The 4 resistors are wired in parallel so that lower power components can be used. E.g 4 1/8W components to deal with 1/2W of power. If you remove all of them you should be able to measure the resistance of a single device. Not sure how you can work out the power rating though.

 

BTW it’s likely that the right most one will also split in two when you try to unsolder it.

 

Regards,

 

John P

 

[Bucoops]

Is this a short?

 

[melmerby]

23 hours ago, jpendle said:

If you remove all of them you should be able to measure the resistance of a single device

Not likely you would get the correct reading if they've been seriously overloaded.

The Left one looks like it's marked 180 which would be 18 ohms (18 ohms & zero multipliers)

 

I notice the two devices of the middle 4 that have lots of solder are 2SD516 which is an NPN transistor, the one above left (both?) , 2SD4189 is an N-Channel Mosfet

 

EDIT incorrect assumption see later post.

Edited May 22, 2023 by melmerby

[skipepsi]

I would send it back to NCE and ask if they can repair it, they do have a good supportive attitude towards customers. 

[Crosland]

I'm 99.9% certain the four-in-a-row resistors are the current sense for the DCC output and you have suffered a catastrophic overload, and let the magic smoke out. It looks like it was in a real hurry to escape one of the resistors. It's mechanical damage only in the sense that the overheating destroyed them. They will not be hard to replace if you can still read the value on one of them, but you need to identify and fix the cause first.

 

After that you may find the output MOSFETs are also blown, even if there's no obvious damage. They are the block of 4-components just above the resistors. They will be much easier to remove with a hot-air de-soldering tool.

[melmerby]

1 hour ago, Crosland said:

After that you may find the output MOSFETs are also blown,                They are the block of 4-components just above the resistors

A change from my previous assumptions, done a bit more digging *

 

From the numbers on the devices we can see :

Bottom Left  D516 = AOD516 = N channel power Mosfet*

Top Left D4189 = AOD4189 = P channel power Mosfet*

The one on it's own is also marked D516 and just possibly also the lower RH one but the crackle effect makes them difficult to read.

 

Assuming it's a typical H bridge output, I would expect 4 Mosfets.

 

They are very high current with low switch on resistance, ideal for the job and maybe still OK

 

* Bit confusing as I've also seen ordinary power transistors with an abreviated number.

 

 

[dasatcopthorne]

Thanks for all the answers everyone.

 

Much appreciated.

 

Dave

[melmerby]

11 hours ago, dasatcopthorne said:

Thanks for all the answers everyone.

 

Much appreciated.

 

Dave

You never told how this came about.

Was it bought like that, or did it fail and had some repairs?

[dasatcopthorne]

2 hours ago, melmerby said:

You never told how this came about.

Was it bought like that, or did it fail and had some repairs?

 

Sorry.

 

I thought I had explained that in the first post.

 

I bought it as faulty knowing it would not work as a true Power Cab but was/is OK as a Slave. Lord knows who or why someone did that to it.

 

I've decided to leave alone for now.

 

Thanks

 

Dave.

 

 

 

 

 

[melmerby]

38 minutes ago, dasatcopthorne said:

 

Sorry.

 

I thought I had explained that in the first post.

 

I bought it as faulty knowing it would not work as a true Power Cab but was/is OK as a Slave. Lord knows who or why someone did that to it.

 

I've decided to leave alone for now.

 

Thanks

 

Dave.

 

Hi Dave, it wasn't obvious to me in your original post.

Presumably it had gone wrong at some time due to a problem and the original owner had found that it was still OK when not required to provide track power.

AS long as the PCB hasn't been badly damaged, it should be repairable if you can identify exactly which components have failed (besides that line of 4 resistors in parallel.)

That would be where I would start.

As I said before, the LH one looks as if it's marked 180 (maybe 130) which would be 18 (or 13 ohms), which if it is in series with theoutput would be a total of 4.65 ohms (or 3.25 ohms)

Both values seem a little high for a current sense dropping resistor. (I would expect maybe a tenth of that value)

Edited May 26, 2023 by melmerby

[melmerby]

Had another look at the picture.

A more logical value marking for those resistors would be 1R0 (1Ω), then 4 would be 0.25Ω.